Automotive air conditioning systems provide driver comfort during driving by cooling air in the vehicle cabin based on a desired cabin temperature. Cabin air is cooled by passing air over an evaporator and directing cooled air to the cabin. Air around the evaporator is cooled when a liquid refrigerant changes into a gaseous form in the evaporator thereby absorbing heat from the surrounding air. The refrigerant vapors from the evaporator then enter a compressor, where it is compressed to a high pressure refrigerant vapor. The pressurized refrigerant vapors from the compressor then enter a condenser, where it is converted into a liquid. The high pressure liquid refrigerant from the condenser is then passed through an expansion valve, where it is allowed to expand to form low-pressure liquid refrigerant, which subsequently enters the evaporator.
In order to maintain normal operation of the air conditioning system, one or more parameters (such as pressure, temperature, etc.) of the refrigerant circulated through the various components of the air conditioning system are monitored based on outputs from one or more sensors. For example, a low side pressure (also herein referred to as compressor inlet pressure) of the refrigerant vapor exiting the evaporator and entering the compressor is monitored by a low side pressure sensor located in the low pressure line delivering refrigerant vapors to the compressor. When the low side pressure decreases below a threshold, it provides an indication that the evaporator is nearing freezing conditions. Therefore, the compressor is turned off to prevent the evaporator from freezing water. In addition, a high side pressure sensor located in the high pressure line delivering pressurized refrigerant vapors from the compressor to the condenser is utilized to monitor a pressure of the high pressure refrigerant vapor (also herein referred to as compressor outlet pressure) exiting the evaporator. When the high side pressure sensor indicates excessive pressure conditions above a threshold outlet pressure, the compressor may be turned off. Further, in some examples, a compressor speed sensor is employed to determine a compressor speed, which may be utilized for diagnosing compressor operation. As such, the compressor may be driven by an energy conversion device, such as an engine or a motor, via a clutch mechanism. Therefore, as an alternative to employing a compressor speed sensor, the compressor speed may be inferred from a speed of the energy conversion device.
However, the inventors herein have recognized potential issues with such systems. As one example, employing two pressure sensors, one in the low pressure line to the compressor and another in the high pressure line from the compressor, increases the cost of the system. Further, employing a compressor speed sensor for compressor speed measurements adds to the system cost, and inferring compressor speed (for example, from engine speed) does not provide accurate results if the clutch fails to engage as commanded and leads to reduced diagnostic efficiency. Still further, as more sensors are used, more interfaces and control strategies are required, which increases system complexity including packaging complexities. Overall, by utilizing three sensors to monitor status of refrigerant circulating through a single compressor, production cost and packaging space are increased, which results in bulky and expensive air conditioning systems.
In one example, the issues described above may be addressed by a method for a vehicle air conditioning system, comprising: disengaging a compressor clutch in response to a compressor inlet pressure below a first threshold pressure; and increasing a condenser fan speed in response to a compressor outlet pressure above a second threshold pressure, both the compressor inlet pressure and outlet pressure based on a pressure sensor located within a compression chamber of the compressor.
In this way, in contrast to utilizing two pressure sensors each located within a high side line and a low side line, a single pressure sensor located within a compression chamber of a compressor is utilized to determine a compressor low side pressure and a compressor high side pressure.
Locating a single pressure sensor within one of the air conditioning compressor's compression chambers may result in a single sensor that has more information on it than conventionally arranged sensors. For example, the compression chamber sees both the low side pressure and the high side pressure at some point in the compression cycle. Therefore, the minimum compression chamber pressure during the compression cycle is indicative of the low side pressure, and the maximum compression chamber pressure during the compression cycle is indicative of the high side pressure. Further, the rate at which the compression chamber pressure varies between maximum and minimum pressure is directly proportional to actual compressor speed. Therefore, the pressure variation is indicative of the actual compressor speed, whether or not the AC compressor clutch is successfully following the command.
As one example, during vehicle operation when the air conditioning system is turned on, an output from a pressure sensor located within a compression chamber of an air conditioning compressor cylinder may be utilized to determine a compressor inlet pressure and a compressor outlet pressure of the compressor. Further, the output from the pressure sensor may also be utilized to determine an operating speed of the compressor. For example, when a compressor piston is on an intake stroke and a suction valve of the cylinder including the piston is open, refrigerant vapors flow into the compression chamber from a suction line (that is, low pressure line) and a pressure of the refrigerant in the cylinder is at the pressure of the refrigerant in the suction line. Therefore, in one example, during a first window of the intake stroke when the suction valve is opened, pressure indications from the pressure sensor may be utilized to determine the compressor inlet pressure. Further, when the compressor piston is on a discharge stroke and a discharge valve of the cylinder is open, refrigerant vapors flow out of the cylinder and a pressure of the refrigerant in the cylinder is at a pressure of the refrigerant in the discharge line (that is, high pressure line). Therefore, during a second window of the discharge stroke when the discharge valve is opened, pressure indications from the pressure sensor may be utilized to determine the compressor outlet pressure. Still further, a duration to complete one cylinder cycle (the duration is also referred to as a rotation period herein) may be determined from the pressure sensor output; and a compressor speed may be determined from the rotation period. Thus, the compressor inlet pressure, the compressor outlet pressure, and the compressor speed may be determined based on output from the pressure sensor located within a compression chamber of the air conditioning compressor.
In another example, the compressor inlet pressure may be determined based on the minimum pressure indicated by the pressure sensor within the compression chamber during the compressor cylinder cycle, and the outlet pressure may be determined based on the maximum pressure indicated by the pressure sensor during the compressor cylinder cycle.
Further, the compressor inlet pressure, the compressor outlet pressure, and the compressor speed may be utilized to monitor operation and/or diagnose abnormal conditions of one or more components of the air conditioning system. As an example, the compressor inlet pressure may be utilized to diagnose an evaporator freezing condition; the compressor outlet pressure may be utilized to diagnose excess outlet pressure conditions, such as those that may arise from engine speed transients; and the compressor speed may be utilized to monitor and/or diagnose a clutch condition, such as whether the clutch is engaged, open or slipping.
In this way, by utilizing a single pressure sensor located within a compression chamber of an air conditioning compressor to determine a compressor inlet pressure, a compressor outlet pressure, and a compressor speed, production cost may be reduced and more compact packaging may be achieved along with improved monitoring and diagnostics.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.